Conventionally, an injection needle assembly is provided with a skin contact portion that allows adjustment of the depth of a needle puncturing in order to stably puncture the skin. Such a configuration makes it possible to reliably penetrate the injection needle to a target depth. Further, such capability of stable puncturing enables stable administration of a medicine into the skin, as described in Japanese Patent Application National Publication No. 2005-527249. An injection needle assembly is connected to a syringe that is to be filled with a medicine, and thus a medicine injection device is assembled.
Air must be exhausted from the syringe, however, before introducing a medicine into it. Thus, a user of the medicine injection device must first perform a procedure to exhaust the air from the syringe, and then introduce the medicine into the device. This procedure or step is referred to as removal of air (“air removal” hereinafter) in which the air contained in the syringe is exhausted.
According to the injection needle assembly set forth in the above-noted Japanese Patent Application National Publication No. 2005-527249, a cylindrical skin contact portion is connected to a needle hub. The skin contact portion is disposed to cover a needle tube, but allows a space between the needle tube and the skin contact portion. Hence, when performing the air removal procedure using such a configured injection needle assembly, not only is the air contained in the syringe exhausted, but the medicine filled in the syringe may also spill from the needle tube and there is a risk of the medicine being held in the space between the skin contact portion and the needle tube.
A problem has thus arisen because the medicine staying in the space between the skin contact portion and the needle tube contacts or attaches to the skin of a user, and causes discomfort to the user when administering the medicine in the injection needle.